In vitro studies will be carried out with microsomes from control and induced (phenobarbital, 3-methylcholanthrene) rat livers and midgut tissues from control and induced (pentamethylbenzene) armyworm (Spodoptera eridania) larvae. Emphasis will be placed on studying the formation of irreversible, inhibitory product adducts with cyto-chrome P-450 in NADPH-reduced microsomoes and on the possibility that the synergists may interact with specific types or pools of cytochrome P-450. The formation of product adducts will be studied by difference spectroscopy and/or the binding of appropriately labeled synergists. The properties of any residual "non-reactive" cytochrome P-450 will be studied by enzymatic assay (epoxidation, hydroxylation and N-demethylation) and a variety of spectral techniques. In vivo studies with rats (or mice) and armyworm larvae will be conducted to determine the formation and reversibility of synergist-chytochrome P-450 complexeS in the intact animal and to evaluate the effects of these complexes on microsomal oxidation. Equilibrium dialysis will be used to study the binding of labeled 1-phenylimidazole to microsomes and to evaluate this ligand as a potential tool for qualitative and qunatitative measurements of different types of cytochrome P-450 in intact microsomes.